Various photographic systems for forming photographic images by diffusion transfer have heretofore been disclosed. Common to such systems, whether black-and-white or color, is that a photosensitive element containing a developable image is developed and an imagewise distribution of image-forming constituents formed as a function of development is transferred to a superposed image-receiver layer to impart thereto the desired transfer image. The image-receiving layer may be separate from the photosensitive element, e.g., contained on a separate support member, or it may be contained on the same support carrying the photosensitive layer or layers. In either instance, the image-receiving layer containing the transfer image may be separated after image formation to provide the photographic print or in lieu thereof, systems are also known wherein the receiving layer is not separated but is maintained in association with the remaining layers of the film unit.
While the present invention is directed to the aforementioned film units in general and systems employing them wherein development is effected in the presence of actinic light, i.e., processing outside the camera, it is particularly directed to so-called integral negative-positive film units for forming color transfer images.
Generally, such film units comprise a plurality of essential layers including at least one light-sensitive silver halide layer and associated dye image-providing material and a dyeable stratum. These essential layers may be contained on a transparent dimensionally stable layer or support member positioned closest to the dyeable stratum. Opacifying means are provided on either side of the photosensitive strata so that the film unit may be processed in the light to provide the desired color transfer image. In a particularly useful embodiment, such opacifying means comprises an opaque dimensionally stable layer or support member positioned on the side of the photosensitive strata opposed from the dyeable stratum to prevent photoexposure by actinic light incident thereon from this side of the film unit and an opacifying agent applied during development between the dyeable stratum and the photosensitive strata, e.g., by including the opacifying agent in a developing composition so applied in order to prevent further exposure (fogging) by actinic light incident thereon from the other side of the film unit when the thus exposed film unit is developed in the light.
While the transfer images obtained from the film unit to which this invention is directed may be separated from the remaining layers of the film unit following development in the light to provide the desired photographic print, of particular interest are those integral negative-positive film units adapted for forming transfer images which are viewable, without separation, as reflection prints.
As examples of such integral negative-positive film units for preparing color transfer images viewable without separation as reflection prints, mention may be made of those described and claimed in U.S. Pat. Nos. 3,415,644, 3,415,645, 3,415,646; 3,473,925; 3,594,164 and 3,594,165; as well as those described and claimed in U.S. Pat. Nos. 3,573,043; 3,573,044 and 3,672,890.
In general, the film units of the foregoing description, e.g., those described in the aforementioned patents and/or copending applications, are exposed to form a developable image and thereafter developed by applying the appropriate processing composition to develop exposed silver halide and to form, as a function of development, an imagewise distribution of diffusible dye imageproviding material which is transferred, at least in part, by diffusion, to the dyeable stratum to impart thereto the desired color transfer image, e.g., a positive color transfer image. Common to all of these systems is the provision of a reflecting layer between the dyeable stratum and the photosensitive strata to mask effectively the latter and to provide a background for viewing the color image contained in the dyeable stratum, whereby this image is viewable without separation from the other layers or elements of the film unit. In certain of these systems, this reflecting layer is provided prior to photoexposure, e.g., as a preformed layer included in the essential layers of the laminar structure comprising the film unit, and in others it is provided at some time thereafter, e.g., by including a suitable light-reflecting agent, for example, a white pigment such as titanium dioxide, in the processing composition which is applied between the dyeable stratum and the next adjacent layer to develop the latent image and to form the color transfer image.
The dye image-providing materials which may be employed in such processes generally are selected from the known materials for use in diffusion transfer which are either (1) initially soluble or diffusible in the processing composition but are selectively rendered non-diffusible as a function of development; or (2) initially insoluble or non-diffusible in the processing composition but are selectively rendered diffusible as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers.
As examples of initially soluble or diffusible materials and their application in color diffusion transfer, mention may be made of those disclosed, for example, in U.S. Pat. Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 2,774,668 and 2,983,606. As examples of diffusion transfer systems employing initially non-diffusible materials, mention may be made of the materials and systems disclosed in U.S. Pat. Nos. 3,443,939; 3,443,940; 3,227,550; 3,227,551; 3,227,552, 3,227,554; 3,243,294 and 3,445,228.
Common to all of the systems is that color transfer image formation is predicated upon a differential in mobility or diffusibility obtained by chemical action as a function of development. This chemical action may, for example, be a redox reaction or a coupling reaction.
Other imaging systems employing other types of reactions, e.g., selective dye formation or destruction, etc. have also heretofore been suggested.
In any of these systems, multicolor images are obtained by employing a film unit containing at least two selectively sensitized silver halide layers each having associated therewith a dye image-providing material exhibiting desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called "tripack" structures employing a blue-, a green- and red-sensitive silver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan dye image-providing material.
A particularly useful system for forming color images by diffusion transfer is that described in U.S. Pat No. 2,983,606, employing dye developers (dyes which are also silver halide developing agents) as the dye image-providing materials. In such systems, a photosensitive element comprising at least one silver halide layer having a dye developer associated therewith (in the same or in an adjacent layer) is developed by applying an aqueous alkaline processing composition. Exposed and developable silver halide is developed by the dye developer which in turn becomes oxidized to provide an oxidation product which is appreciably less diffusible than the unreacted dye developer, thereby providing an imagewise distribution of diffusible dye developer in terms of unexposed areas of the silver halide layer, which imagewise distribution is then transferred, at least in part, by diffusion, to a dyeable stratum to impart thereto a positive dye transfer image. Multicolor images may be obtained with a photosensitive element having two or more selectively sensitized silver halide layers and associated dye developers, a "tripack" structure of the type described above and in various patents including the aforementioned U.S. Pat. No. 2,983,606 being especially suitable for accurate color recordation of the original subject matter.
In the systems described above, for development to be carried out in the light, it has been found to be necessary to include an opacifying agent in the processing composition. This opacifying agent may be the above-mentioned reflecting agent or it may be an additional reagent or mixture or reagents which in combination with the reflecting agent provides the requisite opacity to prevent fogging by actinic light incident thereon, e.g. transmitted through the transparent support member, when the film unit is processed in the light.
In a particularly useful system for initiating development, the processing fluid is applied as the exposed film unit is advanced from the exposing apparatus into the light. This is readily accomplished, for example, by providing the processing fluid, including opacifying agent, in a rupturable container of known description positioned in a processing relationship along a leading edge of the film unit and adapted for spreading of its contents in a substantially uniform layer between selected layers. Suitable pressure means, e.g., a pair of superposed rollers, are provided adjacent the exit passage of the exposing apparatus so that when the film unit is advanced therethrough into the light, the compressive force thus provided ruptures the container and causes spreading of the processing fluid.
In this manner, as the film unit is brought out into the light, the processing fluid containing the opacifying agent has been applied so as to preclude fogging by actinic light incident on the applied layer of processing fluid. However, by a phenomenon sometimes referred to as "light piping" it has been found that some fogging can occur along the rear portion of the film unit, i.e., that portion last removed from the exposing apparatus. This fogging is in no way caused by a defect in the opacifying agent or agents employed, but is caused by light incident on that portion outside the camera being transmitted within the film unit into the exposure apparatus to that portion of the film unit to which the processing composition has not yet been applied and hence is unprotected by the application of the opacifying agent.
To illustrate this phenomenon further, imagine one exposing such a film unit in a camera and then very slowly pulling the film unit through a pair of pressure rollers into the light. As the film unit is thus slowly advanced, the processing fluid is slowly applied so that the portion outside of the camera has the fluid applied and is protected by the opacifying agent while that portion still in the camera has not yet had the fluid applied and is not yet protected from the light, except, of course, for the fact that it is still in the dark chamber of the camera. While light striking that portion of the film unit outside the camera cannot fog those corresponding portions of the film unit, due to the presence of the opacifying agent, a portion of this light may be reflected internally and scatters or diffuses along the film unit to expose and hence fog that portion of the film unit still inside the camera to which the processing fluid has not yet been applied.
While, for purposes of explaining the problem, reference has been made to pulling the film unit very slowly from the camera, it will be appreciated that, because of the great speed of light, no mechanical system yet devised for advancing the film unit is fast enough to prevent this phenomenon from occurring.
It is to this problem to which the present invention is directed.